ECONOMY STUDIOCompound interest calculator
How much your savings grow with monthly deposits, and what the result will really buy after inflation.
- Money you put in
- $58,000
- Interest earned
- $49,563
- What it buys, in today's money
- $64,375
Starting with $10,000 and adding $200 a month at 4.88%, you would have $107,563 after 20 years.
$58,000 of that is money you put in; $49,563 is interest, and interest earned on interest.
With 2.6% inflation a year, $107,563 in 20 years would buy what $64,375 buys today.
At 4.88%, money doubles in about 14.8 years on its own (the "rule of 72": 72 ÷ the rate).
Year by year
| Year | Money in | Interest | Balance | In today's money |
|---|---|---|---|---|
| 1 | $12,400 | $553 | $12,953 | $12,625 |
| 2 | $14,800 | $1,254 | $16,054 | $15,251 |
| 3 | $17,200 | $2,110 | $19,310 | $17,879 |
| 4 | $19,600 | $3,128 | $22,728 | $20,510 |
| 5 | $22,000 | $4,317 | $26,317 | $23,147 |
| 6 | $24,400 | $5,685 | $30,085 | $25,790 |
| 7 | $26,800 | $7,240 | $34,040 | $28,442 |
| 8 | $29,200 | $8,994 | $38,194 | $31,104 |
| 9 | $31,600 | $10,954 | $42,554 | $33,777 |
| 10 | $34,000 | $13,132 | $47,132 | $36,462 |
| 11 | $36,400 | $15,539 | $51,939 | $39,163 |
| 12 | $38,800 | $18,185 | $56,985 | $41,879 |
| 13 | $41,200 | $21,084 | $62,284 | $44,613 |
| 14 | $43,600 | $24,247 | $67,847 | $47,366 |
| 15 | $46,000 | $27,687 | $73,687 | $50,140 |
| 16 | $48,400 | $31,419 | $79,819 | $52,936 |
| 17 | $50,800 | $35,457 | $86,257 | $55,756 |
| 18 | $53,200 | $39,816 | $93,016 | $58,601 |
| 19 | $55,600 | $44,512 | $100,112 | $61,474 |
| 20 | $58,000 | $49,563 | $107,563 | $64,375 |
How it works
Deposits are added at the end of each month, and interest is applied at the compounding frequency you choose (converted to an equivalent monthly rate, so a yearly rate with yearly compounding gives the same yearly result). "In today's money" divides each year's balance by inflation, so you can compare it with prices now.
Why inflation matters: how inflation actually works.
Questions
What is compound interest?
Interest earned on your interest. Each period, interest is added to the balance, so the next period's interest is calculated on a bigger amount. Over long periods the interest can grow larger than the money you put in.
What rate should I use?
It depends on where the money is. For reference: the average savings account pays 0.38%, a 12-month CD 1.76% (FDIC national averages, October 19, 2026), and a 10-year US Treasury note yields 4.88% (November 9, 2026). Investments like stocks can return more or less, and are not guaranteed.
Why show the result in today's money?
Prices rise too. A balance decades from now buys less than the same number of dollars today. The calculator divides by inflation each year; it starts at 2.6%, the average US inflation rate over the last 20 years.
What is the rule of 72?
A shortcut: 72 divided by the yearly rate is roughly how many years it takes money to double. At 6%, about 12 years.
Sources
- FDIC National Rates and Rate Caps
- 10-year Treasury yield (FRED DGS10)
- BLS CPI-U, for inflation (FRED CPIAUCNS)
- SEC Investor.gov, Compound Interest Calculator (method)
Educational tool, not financial advice. Results are estimates from the numbers you enter; lenders and banks calculate in their own ways. Default rates update automatically from official data.